1. Field of the Invention
This invention relates, in general, to electrical apparatus and, more specifically, to vaporization cooled electrical inductive apparatus.
2. Description of the Prior Art
Vaporization cooling systems have been proposed for electrical inductive apparatus, such as power transformers, which utilize a two-phase dielectric fluid having a boiling point within the normal operating temperature range of the electrical inductive apparatus. The dielectric fluid is applied to the electrical inductive apparatus in its liquid state, whereon it evaporates as it contacts the heat producing members and removes heat in quantities equal to the latent heat of vaporization of the dielectric fluid. The resulting vapors are then condensed and reapplied to the heat producing elements in a continuous cycle. In addition to providing cooling, the dielectric fluid also provides the necessary dielectric strength between the electrical elements in its vapor phase at the normal operating temperature and pressure of the electrical inductive apparatus.
Since dielectric fluids having the above-described properties are extremely expensive, economics dictate that such fluids be used in minimal amounts. Thus, prior art vaporization cooling systems utilize relatively small quantities of vaporizable dielectric fluids which are collected in a sump in the bottom of the enclosure and applied to the electrical winding by means of a pump, as shown by U.S. Pat. Nos. 2,961,476 and 3,261,905.
Since the dielectric strength of the vaporizable fluids is directly proportional to the pressure existing within the enclosure, it is common to add a second dielectric fluid, typically a gas which is substantially noncondensable over the operating temperature and pressure range of the apparatus, such as sulfur hexafluoride (SF.sub.6), in sufficient quantities to provide adequate dielectric strength between the electrical elements in the enclosure when the apparatus is deenergized or operating at light loads and substantially all of the vaporizable fluid is in the liquid phase. As the transformer approaches its normal operating temperature, the non-condensable gas must be removed from the enclosure and stored in a separate tank, as shown in U.S. Pat. Nos. 2,961,476 and 4,011,535, since it interferes with the vaporization cooling cycle. Since the non-condensable gas fills a major portion of the enclosure when the apparatus is deenergized or operating at a light load, a storage reservoir or tank, having a large internal volume, is required to store the amount of non-condensable gas originally contained within the transformer enclosure. As the rating and sizes of transformers having vaporization cooled systems have increased, the size of a storage reservoir required for the non-condensable gas also has increased which, therefore, increases the overall size of the electrical inductive apparatus. Although they effectively provide for the separation of the non-condensable gas from the vaporizable liquid, none of the above-cited references provide any means for reducing the size of the storage reservoir required for the non-condensable gas.
Thus, it would be desirable to provide a vaporization cooled electrical apparatus wherein the volume of the storage reservoir required for the non-condensable gas is reduced over prior art apparatus of this type. It would also be desirable to provide a vaporization cooled electrical apparatus wherein more effective use is made of the small quantity of vaporizable dielectric fluid utilized in such apparatus.